Foot orthoses

ABSTRACT

The invention provides an apparatus and method for recording characteristics of a person&#39;s foot and for interpreting the results to design a function foot orthosis. As the person undergoes a movement routine, video cameras (24, 26, 28, 30) view the person&#39;s foot in real time from below, from the front, from the right side and from the rear to produce simultaneous images which together give a three-dimensional record of the person&#39;s foot. During analysis, selected video images from the recordings are calibrated and analyzed geometrically to ascertain the characteristics of the person&#39;s foot. A functional orthotic is designed and manufactured by computer-aided apparatus.

This invention relates to apparatus and methods for use in theprescription, design and production of biomechanical functional footorthoses.

Such orthoses can be used to compensate for, and to control, abnormalmovement of, and within, a person's foot or feet. The orthosis is acustomised insert which fits into the person's shoe or other footwearand is effective in exercising the desired control to the foot.

However, difficulties exist in the current techniques for determiningthe design of an appropriate orthosis to suit an individual foot. If theshape of the orthosis is inappropriate, the orthosis may not achieve thedesired control over the person's foot, and it may even cause distressto the person using the orthoses.

Before an orthosis can be prescribed for a foot, it is necessary tomeasure the characteristics of the foot. This is usually done by aprescribing practitioner identifying predetermined reference points onthe foot and marking these on the skin with a pen. Distances betweencertain points are then measured, and angles between lines joining thepoints are measured with a protractor or other instrument. A majorproblem with this technique is that it can be difficult to determine theexact positions of the reference points to mark on the foot. Furtherinaccuracies are caused by skin movement over the underlying bones ofthe foot, and difficulties in keeping the foot absolutely still in theappropriate position to take the measurements.

In view of the known difficulties in pin-pointing the reference pointson the foot, a system of approximate points has been devised in whichthe points are, in general, easier to determine for each individualfoot. It is then left to the fabrication laboratory at which theorthoses are manufactured to make estimate corrections to themeasurements taken by the prescribing practitioner.

Although this simplifies the procedure for the practitioner, itrepresents a further source of inaccuracy.

When prescribing a design for an orthotic device, the prescriptioninstruction usually comes from a standard neutral position cast(S.T.J.N.) with the forefoot maximally pronated on the rearfoot. Thecast is usually plaster of paris bandage, and the final casting positionis maintained by the prescribing practitioner physically holding theperson's foot in a predetermined position. The neutral position has beendefined as a standard reference position from which the deviation of theperson's foot from "normal" can be quantified.

As an alternative to casting, another known technique involves thepractitioner holding the person's foot in a predetermined stationaryposition while its profile is determined by a scanning laser beam.

Both of the above techniques suffer disadvantages in that they onlystudy the foot in one stationary position. Kinetic measurements, forexample, the range of available movement, cannot be made accurately, andconsequently these have to be estimated by the prescribing practitioner.It can also be difficult, especially with children or with the elderly,to remain absolutely still for long enough to obtain an accurate cast orscan.

In the case of casts, it has been found that up to 75-80% ofprescription casts are incorrect, and have to be corrected at thefabrication laboratories where the functional orthoses are made. Such ahigh rate of error is very unsatisfactory and can lead to further errorsin an attempt to correct the original mistakes.

A further known technique for studying a person's foot is to place smalladhesive pressure transducers on the foot, so as to monitor directly3-dimensional forces with time, as the patient moves about. However, aswell as being incapable of detecting rotational forces, this system issubject to movement of the skin on which the sensors are placed. Thesystem also relies on significant assumptions being made regardingforces within the foot and regarding the position and orientation of thefoot.

Established processes for the manufacture of the orthoses have oftenincluded many process stages, each requiring supervision by controlpersonnel. With such processes it can be difficult to achieve theappropriate material thickness for resilience or rigidity as desired,and to produce an orthotic device which fits the person's foot andfootwear comfortably.

More recently it has been proposed to improve the manufacturing processby using computer-aided modelling and milling. However, current footdiagnosis and measurement techniques still require refinement to matchsuch accuracy.

The present invention has been devised with the above problems in mind.

In a first aspect, the invention provides a method of measuring orthoticcharacteristics of a person's foot, comprising:

providing a plurality of video cameras for viewing the foot from aplurality of different look directions;

recording the shape and appearance of the foot substantially in realtime by using the video cameras concurrently to provide video imagescontaining information in three dimensions; and

analysing the video images to obtain the desired measurements.

By using video cameras, the shape and appearance of the foot can berecorded quickly and easily without requiring the person to hold his orher foot still for long periods of time. The accuracy of the videoimages will depend on the resolution of the cameras, and on theirfocusing. High resolution cameras with auto-focusing are available whichare not too expensive.

Preferably, the video cameras are positioned to view the foot frompositions which are at 90° to the cardinal body planes. The cardinalbody planes correspond to the major axes of the human body, called theTransverse, Frontal and Coronal (or Sagital) directions.

It will be appreciated that any number of cameras may be used asdesired, in order to produce images from desired look directions. Thecameras are preferably adjustable to enable the camera position and lookdirection to be varied as desired.

Preferably the images are analysed and calibrated using a computer basedvideo image processing system. Preferably, the video system allows oneor more of the following functions to be performed: (i) video images canbe stored in a digital framestore; (ii) the images can be viewed in slowmotion, frame by frame; (iii) selected portions of the images can bemagnified or enhanced for contrast; and (iv) the geometry of features inan image can be measured, ie. distances and angles.

Such a system can provide repeatable, accurate measurements withoutrelying on assumptions or approximations as in the prior art. The dataprovided by the measurements and the foot images can easily be put intoa form suitable for three-dimensional modelling for the design of theorthosis.

Preferably, the method includes exercising the foot through a pluralityof predetermined positions and motions, while in the view of thecameras. Thus the method records not only an instantaneous stationaryposition of the person's foot, but also its movement.

Preferably, the exercise includes open and closed kinetic chainpositions. Preferably, the exercise also includes subjecting theperson's foot to controlled stress.

Thus, the method of the invention enables a record to be made of theavailable movement of the foot, and of the foot's appearance orcondition when in various positions.

Preferably, a first of the video cameras is provided to view theunderside of the person's foot. The first video camera may comprise astereo imaging camera to provide a contour image of the sole.

Preferably, a second of the video cameras is provided to view a side, orthe front or the rear of the foot. Several such cameras may be provided,one each to view the front, rear and side of the foot.

One or more (or all) of the cameras may be movable, so that they can beadjusted relative to the person's foot, ie. the camera's position andlook direction may be varied.

Preferably, the output signals of the cameras are combined to form amultiplexed signal containing multiple images. The combined signal may,for example, correspond to four images arranged in four respectivequadrants of a display. The use of a multiplexed signal avoids possibleproblems in time synchronisation which might occur if the images were tobe processed and recorded as separate signals.

Preferably, the step of recording comprises recording the output videosignals, or the combined signal, on to one or more video signalrecording mediums. In the preferred method, a combined output signal isrecorded on to a single recording medium, such as video tape.

Preferably, the method includes indexing the signals recorded on therecording medium or mediums according to a particular foot exercisewhich the person is performing.

For example, the indexing may comprise inserting a code in, or applyinga colour tint or a colour wash to, the signals being recorded.

The method may also comprise presenting a prerecorded demonstrationaudio and/or video recording to instruct the person through a footmovement routine. In such a case, the indexing is preferably controlledby control signals in the prerecorded demonstration recording.

One of the cameras may comprise a thermal camera to detect "hot spots"on the patient's body. As a further alternative a dedicated thermalcamera could be provided in addition to the above cameras.

In a second closely related aspect, the invention provides a method formaking a record of a person's foot for a functional orthosis, comprising

providing a first video camera to view the foot from the underside;

providing a second video camera to view the foot from the rear;

providing a third video camera to view the foot from a side;

providing a fourth video camera to view the foot from the front; and

recording the shape and appearance of the foot substantially in realtime by using the video cameras concurrently to provide video imagescontaining information in three dimensions.

Preferably one or more (or all) of the cameras are movable so that theycan be adjusted relative to the person's foot. Preferably, the camerasare positioned or adjusted to view the foot from positions which are at90° to the cardinal body planes.

Preferably, the method includes exercising the foot through a pluralityof predetermined positions, motions and stresses, as explainedhereinbefore.

Preferably, the method further comprises combining the output signalsfrom the cameras to form a multiplexed signal containing multipleimages, as explained hereinbefore.

Preferably, the method further comprises indexing the signals, forexample by using a colour tint, as explained hereinbefore.

Preferably, the method further comprises presenting a prerecordeddemonstration film to instruct the person through a foot movementroutine. In such a case, the indexing is preferably controlled from thedemonstration film.

The method may also comprise providing controlled lighting to illuminatethe person's foot during recording. The lighting may be controlled to bevaried during the recording process to provide optimum lighting for theperson's particular foot position or foot exercise. For example, incertain cases it might be found that light shining into a camera fromthe opposite side of a person's foot can "blind" the camera, or reduceits effective contrast. An example of a possible problem might beilluminating the person's foot from above when it is desired to obtaindetail of the underside of the person's foot. In such a case, it wouldbe desirable to illuminate the person's foot from below rather than fromabove. Therefore, the method may comprise providing light from onedirection during certain intervals of the recording process, andproviding light from one or more other directions during one or moreother intervals. Preferably, the method further comprises controllingthe lighting in response to control signals in the prerecordeddemonstration recording.

Preferably, the method further comprises providing visual markers on theperson's foot. For example, manual stick-on markers or a marker sheetcould be used. Alternatively, the method may comprise projecting lightmarkers or light-shadow markers on to the foot. For example, a gridarrangement of dots could be projected to create a grid image of dots onthe person's foot. Such an arrangement could provide additionalreference points to enhance the visibility during the analysis of thevideo recordings, also to enhance the 3-dimensional shape of the foot,and to assist in pinpointing the precise position of selected points onthe foot. Preferably, the method further comprises controlling theprojection of visual markers in response to signals in the prerecordeddemonstration recording.

The light sources for the lighting and for the light projection may bechosen as desired to produce the appropriate lighting effect. Forexample, laser lighting or projection may be used.

Preferably, the method comprises recording the video images on a videorecording medium, either separately or as multiplexed signal. The lattersignal avoids the possibility of time synchronisation problems duringplayback.

In a third closely related aspect, the invention provides an apparatusfor making a record of a person's foot for a functional orthosis,comprising:

a platform on which a person may stand or may place the foot to berecorded, at least a portion of the platform being transparent;

a first video camera at a first position to view the underside of thefoot through the transparent portion of the platform;

a second video camera at a second position for viewing the foot from therear;

a third video camera at a third position for viewing the foot from aside;

a fourth video camera at a fourth position for viewing the foot from thefront; and

means for operating the cameras concurrently for recording the shape andappearances of the foot substantially in real time to provide videoimages containing information in three dimensions.

Preferably, at least the second, third and fourth video cameras aremovable relative to the platform so that they can be positioned relativeto the person's foot at optimum orientations to view the foot from therear, side and front, respectively. Preferably, the cameras view thefoot from positions which are at 90° to the cardinal body planes.

This enables account to be taken of the different feet positions whichpeople adopt. For example, one person may stand naturally with his orher feet splayed outwardly, while another person may stand with his orher feet parallel. In the preferred embodiment, the second, third andfourth cameras are in fixed angular positions relative to each other,spaced apart by about 90°. This ensures that when, for example, thesecond camera is positioned appropriately to view the rear of the foot,the third and fourth cameras will be lined-up automatically to view theside and front of the foot, respectively. The cameras are capable oflimited arcuate movement together around the intended position of theperson's foot on the platform. Preferably, all the cameras are movable.Preferably each camera can be adjusted to view in any selecteddirection.

Preferably, at least one of the second, third and fourth video camerasis capable of being inclined relative to the platform to view along anelevated look direction, for example, up to the person's knee. Thisenables the person's lower body movement to be observed during the footexercises, which can give information about abnormalities in gait andstance.

Preferably, the platform is marked with a graticule grid. This canassist in calibrating the video images during analysis.

Preferably, the apparatus comprises a multiplexer for combining thesignals from the video cameras to form a multiplexed signal. Forexample, the images in the four video signals may be reduced in size,and multiplexed to appear in respective quadrants of a combined "frame".

Preferably, the apparatus further comprises indexing means for applyingor inserting an index code or signal to one or more of the four videosignals. The index code or signal indicates which particular form offoot exercise was being performed at the time the images were recordedby the video cameras. In the preferred embodiment, the indexing meansapplies a colour tint to the video images, the colour being variable.

Preferably, the apparatus further comprises an audio/video monitor and aplayback apparatus for presenting a pre-recorded demonstration orinstruction film to guide the person through a pre-planned foot movementroutine. Preferably, the apparatus comprises means responsive to controlsignals in the pre-recorded film to control the index signal applied bythe indexing means.

Preferably, the apparatus comprises means for recording the video imagesignals, or the multiplexed signal, on a video recording medium. In thepreferred embodiment, the multiplexed signal is recorded on to a singlerecording medium, such as video tape.

The first video camera may comprise a stereo imaging camera to provide athree dimensional contour image of the sole of the person's foot. Theoutput signal from the camera would include a colour componentindicative of the distance from the camera. The indexing means wouldthen be controlled not to adjust the colour component from the firstcamera.

More than four video cameras may be provided, as desired. For example,if detail of the person's upper body movement is required, additionalcameras may be used to record this.

A treadmill or a walkway may also be used in association with therecording apparatus, in order to observe a person's foot movement whilewalking or running. To avoid vibrations being transmitted to the videocameras which could introduce image jitter, the cameras might beisolated from the treadmill or walkway, for example, using vibrationabsorbing supports.

Preferably, the apparatus further comprises controllable lighting toilluminate the person's foot. Preferably, the lighting comprises meansfor providing light to illuminate the foot from a plurality ofselectable directions. For example, this may comprise a firstcontrollable light source for illuminating the foot from above, and asecond controllable light source for illuminating the person's foot frombelow. Preferably, the apparatus further comprises means for controllingthe lighting in response to control signals in the pre-recorded film toprovide fixed or varying lighting to suit each particular foot exercisebeing performed. A manual control could also be provided.

To improve the 3-dimensional accuracy of the calibration and analysis,visual markers may be arranged on the person's foot. For example, manualstick-on markers or a marker sheet could be used. Alternatively,light-shadow markers could be projected onto the foot by means of alight projector. The markers would provide additional reference pointsto enhance visibility during the analysis of the video recordings, alsoto enhance the 3-dimensional shape of the foot, and to assist inpin-pointing the precise position of selected points on the foot.Preferably, the apparatus comprises a light, or light-shadow, imageprojector which is controlled in response to control signals in thepre-recorded film. A manual control could also be provided.

Preferably, the apparatus comprises means for identifying the regions ofcontact of a person's foot on the platform. In a preferred form, suchmeans comprise means for illuminating the platform in such a manner thatthe areas of contact are highlighted when the foot is in view from belowthe platform. Preferably, the apparatus comprises means for introducinglight into the transparent portion of the platform, such that the lightwill be refracted/reflected differently at the "foot contact" areas inorder to produce a different visual effect at these contact areas. Inthe preferred embodiment, the platform is made of perspex, and light isintroduced at one edge of the platform to illuminate the material withinthe platform. When a person stands on the platform, the areas of contactappear as significantly lighter regions, whereas regions where there isno genuine contact appear as normal brightness. The effect is believedto result from the contact or pressure of the person's foot whenstanding on the platform affecting the interior and surfacerefraction/reflection characteristics of the material, which in turnproduces a light image pattern. Materials other than perspex (eg.acetate) may be used to form the platform while still achieving the samevisual effect.

The above principles of the invention also permit new techniques foranalysing details of a person's foot.

In a fourth aspect, the invention provides a method for determiningcharacteristics of a person's foot, comprising:

providing a sequence of video images frame by frame of a person's foot;

selecting a frame for analysis;

defining predetermined points on the image depicted in the frameselected for analysis; and

calculating mathematically one or more geometric characteristics of theperson's foot based on the points defined in the image.

Thus, the values of predefined geometric characteristics or parameterswhich describe a person's foot can be calculated by measuring points onthe video image of the person's foot. The method allows a particularframe to be selected which typifies the optimum shape or position of thefoot for calculating a characteristic.

In the preferred embodiment, the step of calculating is performedautomatically within a computer based video image processing system. Theaccuracy is determined by: (i) the resolution of the image frame; (ii)the resolution of the computer based system; and (iii) the calibrationof the system for measuring distances between selected pixel points inthe video image.

Preferably, to achieve accurate calibration, at least one of the videoframes includes a linear calibration scale relating to the size of thefoot depicted in the video images and the method includes obtaining acalibration from the calibration scale prior to calculating the one ormore characteristics.

Preferably, each video frame or "instant" includes a plurality of imagesdisplayed concurrently and obtained from different look directions, andthe method comprises selecting a frame for analysis based on a first ofthe plurality of images, and using a second of the plurality of imagesto calculate the one or more characteristics. By this method, it ispossible to select only the appropriate frames, which satisfy severalcriteria to obtain accurate measurements.

In a fifth aspect, the invention provides apparatus for determiningcharacteristics of a person's foot comprising:

means for providing a sequence of video images of the foot frame byframe;

means for selecting a frame for analysis;

means for defining predetermined points on the image depicted in theframe selected for analysis; and

means for calculating mathematically one or more characteristics of theperson's foot based on the points defined in the image.

Preferably, each frame includes a plurality of images, and the means forselecting comprises means for selecting one or more of the images foranalysis from the frame.

Preferably, the apparatus comprises a digital pixel framestore in whichthe video frame or a selected video image is stored.

Preferably, the apparatus comprises a plurality of framestores in whichvideo frames or selected video images can be stored for later use.

In a further aspect, the invention provides a method of diagnosingorthotic characteristics of a person's foot, comprising:

providing a sequence of video images frame by frame of the foot;

measuring geometric characteristics of the foot from one or more of thevideo frames; and

comparing the measured geometric characteristics with a set of referencecharacteristics to determine deviation from normality.

Preferably the method further comprises operating an expert system toanalyse the measured geometric characteristics, and to prescribe afunctional orthosis.

An embodiment of the invention is now described by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a process for prescribing/manufacturingfunctional orthoses;

FIG. 2 is a schematic side view of an apparatus for making a record of aperson's foot;

FIG. 3 is a block diagram of parts of the apparatus of FIG. 2;

FIG. 4 is a block diagram of an apparatus for analysing the results fromthe apparatus of FIG. 2;

FIG. 5 is a block diagram of the process for operating the apparatus ofFIG. 4;

FIGS. 6 and 7 are diagrammatic views illustrating geometric analysis ofa sample image.

FIG. 1 illustrates a process in accordance with this invention, foranalysing a person's foot or feet, and for prescribing and manufacturingone or more suitable functional orthoses for that person.

The first stage 10 of the process is to make a record of each foot usinga plurality of video cameras making simultaneous recordings fromdifferent look directions. As described below in more detail, thecameras run in real time, and are positioned to enable the movement,shape and appearance of foot to be viewed substantiallythree-dimensionally.

The second stage 12 of the process is to analyse the video recordings,and measure the geometric characteristics of each foot as seen in thevideo images. As described below in more detail, this involves selectingspecific recorded images in which the foot is in one of a plurality ofpredetermined reference positions. The geometric characteristics canthen be calculated by a computer-aided geometric analyser. Once thecharacteristics have been determined, an "expert system" is used toanalyse the results, and to supply the appropriate design parameters forone or more compensatory functional orthoses.

The final stage 14 of the process is to manufacture each orthosis byusing a computer controlled milling or manufacturing machine. The datafor the machine can be supplied directly as a three-dimensional modelcalculated by the expert system, based on the shape of the person's footas viewed in the video images. As an alternative, a manual manufacturingprocess could be used based on the data obtained from the recordedimages.

FIGS. 2 and 3 illustrate an apparatus 20 for making the video recordingof a person's foot. The apparatus 20 includes a transparent platform 22on which the person stands barefooted. A first video camera 24 ismounted below the platform 22 in a first position to view the undersideof the person's foot. A second video camera 26 is mounted at the levelof the platform 22 in a second position to view the foot from the front.A third video camera 28 is mounted at the level of the platform 22 in athird position to view the foot from one side. A fourth video camera 30is mounted at the level of the platform 22 in a fourth position to viewthe person's foot from the rear.

In this exemplary embodiment, the cameras 26, 28 and 30 above theplatform 22 are movable in a plane substantially parallel to theplatform 22. Each camera 26, 28 and 30 is mounted on a respectivesupport 32 which extends through a respective arcuate slot (not shown)in the platform, such that the cameras are movable arcuately around theperson's foot. The cameras 26, 28 and 30 are coupled for movementtogether to maintain their orientations relative to one another, and therange of movement is about 90°. In other embodiments, the cameras may becapable of other forms of movement relative to the platform, andrelative to one another. In use, the cameras are positioned so that theyview the foot from user selected positions, for example, at 90° to thecardinal body planes.

The camera 24 positioned below the platform 22 may comprise a stereoimaging camera which provides a 3-D contour of the surface being viewed,in this case the underside of the person's foot. The output from thestereo imaging camera may, for example, include a colour componentindicative of the distance from the camera.

The camera 26 for viewing the person's foot from the front is preferablycapable of viewing the person's leg up to and including the knee. Thisallows a record to be made of the person's stance, and gait when moving.The camera 26 is preferably inclinable so that its field of view can beelevated above the level of the platform. The other two cameras 28 and30 above the platform may also be inclinable.

For maximum flexibility, the horizontal and vertical position of eachcamera, its rotational direction and its inclination, may be adjustableas depicted by the arrows 31 and 33.

A light projector 25 (not shown in FIG. 2) is provided to project lightonto the underside of the person's foot. The projector may include adevice to project markers in the form of light-shadows at predeterminedpositions. The projector is preferably adjustable to suit the sizes andshapes of different people's feet.

A second light projector 27 (not shown in FIG. 2) is provided to projectlight onto the person's foot from above. The light projectors 25 and 27are controlled by a controller 29, described in more detail below.

The platform 22 is marked with a graticule grid (not shown) which isused for the purpose of calibrating the video images, and to permitcalibrated stress measurements, as explained in more detail hereinafter.

In this exemplary embodiment the platform is made of transparentperspex, and comprises a slab or sheet approximately 2.5 cm (1 inch) inthickness. A light source 35 is arranged adjacent to one edge of theplatform 22 in order to introduce light into the interior of theplatform 22. This provides a visual effect to locate precisely theregions at which the person's foot is in contact with the platform 22.It is believed that the contact and/or pressure of the foot affects theinternal and/or surface refraction/reflection characteristics of thematerial. The result is that the contact areas become significantlylighter (i.e. white) regions when viewed from below, and the surroundingnon-contact region show as regions of normal brightness. It is thuspossible to identify or record accurately which parts of the foot areflat against the platform, and which parts of the foot are not incontact. The light source 35 can be controlled automatically, asdescribed hereinafter.

A guard rail 34 is provided around the platform 22 to prevent a personstanding on the platform 22 from accidentally falling off whenperforming foot exercises.

An audio video monitor 36 is mounted on a movable arm or stand 38 infront of the platform 22. In use, a prerecorded demonstration orinstruction film is presented on the monitor 36 from a video tape player40. The film guides a person standing on the platform 22 through aseries of pre-planned foot exercise routines. The video cameras 24, 26,28 and 30 record the movement, shape and appearance of the person's footsubstantially in real time as the person performs the routines. Theroutines are intended to put the person's foot through a range ofstationary and kinetic positions, both stressed and unstressed,preferably using the whole range of available foot movement.

In this exemplary embodiment, the film also includes one or more controlsignals which are used to control operation of the recording apparatusduring different intervals of the foot routine. An output from the tapeplayer 40 is coupled to an input of the controller 29 to achieve this.As the demonstration film is run, the controller 29 receivesinstructions from the control signals encoded in the film to control thelight projectors 25 and 27 to provide optimum lighting (andlight-markers when appropriate) for the foot routine being performed,and also signals to control operation of the light source 35. Thecontroller 29 also provides index control signals to control an indexer46 described below.

The video cameras 24, 26, 28 and 30 have a high enough resolution torecord the person's foot accurately. The frame scanning period for eachcamera should be as fast as possible so that blurring will not occurduring foot movement. A scanning interval of about one thousandth of asecond is appropriate. The frame rate for each camera should also behigh, so that foot movement is recorded accurately. A frame rate ofabout 25 frames per second is acceptable. The cameras may be monochromeor colour, but it has been found that monochrome images may be easier toindex and to analyse, as described hereinafter.

The output signals from the cameras 24, 26, 28 and 30 are fed to asignal multiplexer 42, which provides a single combined output signal.As illustrated at 44, the images from the cameras (labelled 1-4) areeach reduced to a quarter of the frame size, and are arranged inrespective quadrants of the frame. Therefore, each video frame of thecombined output signal comprises the four camera images displayedconcurrently. Depending on the number of video cameras being used, themultiplexer 42 may function to combine a greater (e.g. 8) or lesser(e.g. 2) number of signals into a single output signal.

The output from the signal multiplexer 42 is fed to an indexer 46 whichinserts or applies an indexing signal or code to one or more of the fourimages in the frame. The index is used to identify which foot routinethe person is performing at the time of recording. An output from thecontroller 29 is fed to a control input of the indexer 46 to controlthis. In the present exemplary embodiment, the indexer 46 applies acoloured tint to the video signal, the colour being variable andrepresenting which foot routine is currently being performed. The use ofa colour tint has the advantage that it does not interfere with theinformation content of the monochromatic signals, it can be easilyrecognised, and it does not require part of the useful video signal tobe set aside for a dedicated index code. If a stereo imaging camera isused, the indexer would be arranged not to adjust the colour componentof the image from the stereo imaging camera. As an alternative, the tintmay be replaced by text or graphics (eg. a barcode) to indicate thecurrent foot routine.

The output video signal from the indexer is ready to be analysed. Inthis embodiment, the signal is recorded on a high quality videorecording medium, such as Hi-8, S-VHS or VHS tape. In other embodiments,the signal may be processed further, for example by a computer on theapparatus, or it may be transmitted directly to an external analysisstation, for example, by a modem link.

It is also envisaged that the signal may be transmitted directly over avideo cable, or transmitted as a telephone/video signal to a remotestation for analysis, or transmitted or recorded as computer data orgraphics data.

Various systems and apparatus may be used to analyse the videorecordings. The degree of complexity and automation of the analysis willdepend on the required accuracy of the measurements and on whether ornot the analysis is to be performed by an operator skilled inbiomechanics. The video recordings made by the recording apparatus lendthemselves to analysis by a computer aided graphics system.

FIG. 4 illustrates one form of apparatus 48 for analysing the videorecordings. It includes a video tape player 50 for playing back the taperecorded with the apparatus of FIG. 2. One or more additional, oralternative, video or graphics information inputs (not shown) may beprovided (for example, a modem link) depending on how the video signalrecorded above is to be forwarded or sent for analysis.

The apparatus 48 comprises a digital display framestore 52 into whichthe video signal is fed. The display framestore 52 provides an output toa video monitor 54 for display. The apparatus also comprises a bank ofmemory framestores 56 in which a number of video frames can be stored,and an image selector/magnifier 58 which can process video data toselect, enlarge or reduce portions of the video frame. The apparatusalso comprises a computer-aided geometry analyser 60 which can calculatedistances and angles between selected points and lines marked on thevideo images.

The apparatus also includes a database memory 62 for storing sets ofresults for a particular person, calculated by the geometry analyser 60.

The apparatus 48 operates under the control of a controller 64. Thisincludes a manual input means (not shown) for example, in the form of akeyboard or a computer mouse by which a person can input commands tocontrol the apparatus.

The apparatus of FIG. 4 may be embodied as dedicated digital processingand video processing circuitry. It may also be embodied by a programmedcomputer with a graphics capability configured to perform the above, orby a combination of a computer and dedicated graphics circuitry.

In use, referring to FIGS. 4 and 5, the process of analysis begins byselecting a number of frames from the input video signal, which are tobe used for analysis. Each frame includes approximately four concurrentimages. The selection is achieved by an operator viewing the videosignal in slow motion, frame by frame, for example by using thecontroller 64 and the display framestore 52.

The operator selects frames in which the foot is in one of a pluralityof predetermined reference positions which illustrate the behaviour ofthe foot. Such positions include the sub talor joint neutral positionwhich is used conventionally for making casts, but they also includeother positions from which the range of foot movement and thecharacteristics of foot under different stationary/kinetic conditionscan be observed.

The four concurrent images in each frame enable the operator to observethe foot from different directions, effectively in three dimensions.Thus the operator can select the individual frame or frames in which thefoot is in precisely the correct position for analysis.

It will be appreciated that if only one image was being viewed, it mightbe difficult for the operator to decide which frame represented theprecise moment when the foot was in one of the reference positions. Forexample, by referring to the front view only, it is difficult to detectwhen the heel of the foot is pressed down. However, by displayingsimultaneously the recorded views from the different directions, i.e.from the front, rear, side and underneath, it is possible to determineaccurately the foot's position in three dimensions. Frames which areselected for later use can be stored in the memory framestores 56.Typically about 30 frames would be selected at this stage.

The next stage is for the operator to select specific images foranalysis from the frames selected in the above procedure. Under thecontrol of the controller 64, the operator can select one or more imagesfrom each frame for further analysis. Typically, the images will beselected using the selector/magnifier 58.

For each frame, it is likely that only one, two or perhaps three of thefour images will contain geometric information of interest. The fourimages when viewed together determine the precise position of the footat that instant, but not all of the four images may be suitable forgeometric analysis.

Each selected image should be magnified so that it occupies the whole ofthe available display area of the monitor 54 (and of the displayframestore 52). If only a portion of a selected image is required forfurther analysis, that portion should be further magnified to occupy thewhole of the display area, and the remainder of the image can becropped. The selected images can then be restored, for example, in thememory framestores 56. Typically about 40 images would be selected.

The next stage in the analysis is for each selected image to be studied,and the geometric details to be measured. This can either be donemanually, automatically or semi-automatically with the assistance of theoperator. Before each image can be studied, the geometry analyser has tobe calibrated according to the scale of the video image. Calibration isbased on the graticule grid pattern of the platform 22 which will beincluded in the recorded video images.

During semi-automatic operation of the geometry analyser 60, theoperator identifies the position of certain key points on the image ofthe foot as viewed on the display framestore 52. The operator may selectthese points by moving a computer-mouse which controls a positioncursor, or a line cursor, on the displayed image.

FIGS. 6 and 7 illustrate one form of geometric analysis on a rear-viewimage of a person's foot using semi-automatic operation. In FIG. 6 aline cursor 70 is moved to a first point 72 at which the Achilles'tendon meets the heel bone as viewed in the displayed position. A secondline cursor 74 parallel with the front is drawn on the imageautomatically by the geometric analyser. The operator marks the "edgedefinition" point "X" on the image at which the cursor lines 70 and 74meet the edge of the image. Once these points have been entered, thegeometric analyser calculates mathematically the Tibial Varum Angle, seeFIG. 7. The calculation is performed automatically by (i) calculatingthe midpoint 76 between the edge definition points "X" marked for thefirst line cursor 70; (ii) calculating the midpoint 78 between the edgedefinition points "X" marked for the second line cursor 74; (iii)constructing a bisector line 80 passing through the midpoints 76 and 78calculated above; and (iv) measuring the angle which the bisector line80 makes with an imaginary vertical line.

Referring again to FIG. 6, the positioning of two more line cursors 82and 84 (the latter being drawn and positioned automatically relative tothe first) is used to determine the Varus and Valgus angles for thefoot. In a similar manner to that described above, the operator marksthe "edge definition" points "X" at which the line cursors 82 and 84meet the edge of the image. The geometric analyser calculates themidpoints between the "edge definition" points, constructs a bisectorline 86, and measure the angle between the bisector line 86 and thevertical.

For fully automatic operation, a recognition database 66 will beprovided to provide recognition information to the apparatus to enablethe reference points on the image to be located automatically. Inparticular, the system may be programmed to detect or determine theedges of a person's foot in the recorded image, and to generate asurface contour representation of the three-dimensional shape of thefoot contained in the images. Thus, the amount of any external inputrequired from the operator can be reduced to a minimum for geometricanalysis.

In short, it will be apparent to the skilled man that at least the samedegree of geometric information can be obtained from the images as wouldbe obtainable from conventional foot-casting techniques. It will beapparent to the skilled man precisely what information is required inorder to define an appropriate functional orthotic. However, with theinvention, the amount of information made available by the use of thecameras far exceeds the amount of information derivable by conventionalcasting techniques.

Since the memory framestores 56 can hold quite a large number of images,the geometric analysis for certain characteristics may be repeatedseveral times using different images. The results can then bestatistically averaged to improve the accuracy of the determinations.This will be particularly advantageous in cases where it is apparentfrom the video images that critical joints of the foot are incapable ofadequate motion. Characteristics may be calculated in differentpositions of the foot, and the results compared with each other.

The results can be fed into the information database 62 in whichinformation is collected for each of the person's feet.

The characteristics may then be fed to an expert system 68 which isprogrammed to deduce from the measured characteristics appropriateparameters for a functional orthosis to match the foot being studied.The expert system assesses the degree to which the foot deviates from anormal or ideal foot, and also assesses the amount of orthotic controlthe foot requires. It also assesses the amount of control the foot iscapable of accepting. The expert system may be implemented entirely witha programmed computer, or it may be an interactive computer-aided systemwhich is operated by a skilled practitioner.

The expert system 68 provides as its output the prescription data forthe design and shape of a pair of functional orthoses, each one beingcustomised to match an individual foot. In this exemplary embodiment,the output data is provided in the form of a three dimensional datamodel for each orthosis. Thus the system of the preferred embodiment isable to take advantage of the recent developments in computer-aidedmanufacture (CAM). The precise form of the data for thethree-dimensional model will depend on the requirements of themanufacturing machines, but one form which is envisaged in particular isa "wire-cage" representation defining the outline in three-dimensions.

In one type of manufacturing process, the orthotic device is milled froma carbon-epoxy block rather than by using more conventionalthermoplastics. Using the 3-dimensional prescription data, an accuratereplica article can be manufactured automatically and as a relativelyquick process. The article can be milled down to give the appropriatethicknesses for resilience/rigidity as prescribed for the person's foot.

It will be appreciated that other manufacturing processes (includingmanual processes) could be used for the fabrication of each orthoticdevice. However, the present invention lends itself to being able toprovide the appropriate prescription and design information in a formmatched to a particular fabrication system.

It will be appreciated that the technique of the present invention torecord a person's foot by using video camera positioned to obtainthree-dimensional information enables simple and accurate measurementsto be taken from a person's foot. It avoids the need for majorassumptions and approximations as used in the prior art. The operatordoes not need to be skilled in the art of biomechanics. Also, thetechnique does not rely on difficult co-operation from the person who'sfoot is being analysed, and in particular it avoids the need for theperson to have to remain in a predetermined position without movement.

During analysis, the images of the foot can be "frozen" at precisely theright moment which provides ideal geometric characteristics formeasurement and analysis. Using computer-aided technology, measurementscan be made much more accurately than with the manual protractor typemethods used in the prior art. Finally, it is possible to study the footin any of the positions in which it has been recorded, to observe rangeof movement and abnormal joint behaviour.

As a modification to the embodiment described above, a thermal cameramay be provided to detect "hot spots" on the person's foot or other partof the body. The thermal camera may be included as an integralthermal/video camera in the place of one of the video cameras, or it maycomprise a separate dedicated camera providing an additional recordingsignal.

As shown phantom in FIG. 2, one or more further video cameras 90 may beprovided to view middle and upper portions of the person's body as theperson performs the foot exercises. Such additional cameras may beuseful for observing shoulder, spinal and general back motion, forexample, for a chiropractor. The cameras 90 may be adjustable to view atany angle of elevation, and in any direction as desired. The signalsfrom the further cameras may be multiplexed and indexed with the signalsfrom the foot cameras, or it may be recorded and processed separately.

The technique of this invention also permits the design of thefunctional orthotic to be matched to different footwear required by thesubject person. For example, individual devices may be required forsports footwear, dress footwear, and casual footwear. The inventionpermits functional orthotics to be adapted to the "footwear"characteristics as well as to the orthotic characteristics of theperson's foot.

Although in the embodiment described above, the control of the lightingprojectors 25 and 27, and of the indexer 46 is performed automatically,it will be appreciated that the control may have a manual override, orit may be entirely manual.

It will also be appreciated that in accordance with the principles ofthe present invention (particularly as described in the preferredembodiment) a person's foot can be measured, and an orthotic deviceprescribed, with a much greater accuracy and reliability than with someconventional methods. The "weak points" of the conventional methods canthereby be avoided to improve the standard of quality.

It will be appreciated that the above description of the invention ismerely illustrative of a preferred embodiment, and modifications ofdetail may be made without departing from the scope, or principles orspirit of the invention.

We claim:
 1. A method of measuring orthotic characteristics of aperson's foot, comprising:projecting a pattern of light markers onto thefoot; providing a plurality of video cameras for viewing the foot from aplurality of different look directions; recording the shape andappearance of the foot substantially in real time by using the videocameras concurrently to provide video images containing information inthree dimensions; and analysing the video images to obtain the desiredmeasurements.
 2. A method according to claim 1, wherein the cameras viewthe foot from positions which are substantially at 90° to the cardinalbody planes.
 3. A method according to claim 1 or 2, wherein the camerasare positioned to view the foot from one or more of: below the foot; infront of the foot; behind the foot; at the side of the foot.
 4. A methodaccording to claim 1 or 2, wherein the step of analysing comprisesdigitising at least some of the video images, and utilising a computeraided graphics system to analyse at least some of the digitised images.5. A method for making a record of a person's foot for a functionalorthosis, comprising:projecting a pattern of light markers onto thefoot; providing a first video camera to view the foot from theunderside; providing a second video camera to view the foot from therear; providing a third video camera to view the foot from a side;providing a fourth video camera to view the foot from the front; andrecording the shape and appearance of the foot substantially in realtime by using the video cameras concurrently to provide video imagescontaining information in three dimensions.
 6. A method according toclaim 5, further comprising multiplexing the signals from the cameras toprovide a single combined signal.
 7. A method according to claim 6,further comprising recording the combined signal on a video signalrecording medium.
 8. An apparatus for making a record of a person's footfor a functional orthosis, comprising:a platform on which a person maystand or may place the foot to be recorded, at least a portion of theplatform being transparent; means for projecting a pattern of lightmarkers onto the foot; a first video camera at a first position to viewthe underside of the foot through the transparent portion of theplatform; a second video camera at a second position for viewing thefoot from the rear; a third video camera at a third position for viewingthe foot from a side; a fourth video camera at a fourth position forviewing the foot from the front; and means for operating the camerasconcurrently for recording the shape and appearances of the footsubstantially in real time to provide video images containinginformation in three dimensions.
 9. Apparatus according to claim 8,further comprising a multiplexer for combining the signals from thecameras to provide a single combined signal.
 10. Apparatus according toclaim 9, further comprising means for recording the combined signal on avideo signal recording medium.
 11. Apparatus according to claim 8, 9 or10, further comprising means for indicating the contact regions of aperson's foot when the person is standing on the platform.
 12. A methodfor determining characteristics of a person's foot,comprising:projecting a pattern of light markers onto the foot;providing a sequence of video images frame by frame of said foot;selecting a frame for analysis; defining predetermined points on theimage depicted in the frame selected for analysis; and calculatingmathematically one or more geometric characteristics of the person'sfoot based on the points defined in the image.
 13. A method according toclaim 12, wherein the video images are digitised.
 14. A method accordingto claim 12 or 13, further comprising a step of calibrating the videoimages based on a marker or scale contained in at least one image.
 15. Amethod according to claim 12, 13 or 14, wherein each frame comprises aplurality of concurrent images corresponding to different simultaneousviews of a person's foot, and the method further comprises selecting atleast one of the images for analysis from the plurality of images. 16.Apparatus for determining characteristics of a person's foot,comprising:means for projecting a pattern of light markers onto thefoot; means for providing a sequence of video images of the foot frameby frame; means for selecting a frame for analysis; means for definingpredetermined points on the image depicted in the frame selected foranalysis; and means for calculating mathematically one or morecharacteristics of the person's foot based on the points defined in theimage.
 17. Apparatus according to claim 16, further comprising means forcalibrating the mathematical calculating means based on a marker orscale contained in at least one image.
 18. Apparatus according to claim16 or 17, wherein each frame comprises a plurality- of concurrent imagescorresponding to different simultaneous views of a person's foot, andthe apparatus further comprises means for selecting at least one imagefor analysis from the plurality of images.
 19. A method of measuringorthotic characteristics of a person's foot, comprising:projecting apattern of light markers onto the foot; providing a sequence of videoimages frame by frame of the foot; measuring geometric characteristicsof the foot from one or more of the video frames; and comparing themeasured geometric characteristics with a set of referencecharacteristics to determine deviation from normality.